1. Field of the Invention
The present invention relates generally to nuclear reactor facilities, and more particularly to a new and improved nuclear reactor pressure vessel closure head assembly which is structurally modular, and wherein the structural principles of the same are applicable to existing or current nuclear reactor facilities in accordance with retrofitting techniques, whereby all major components operatively associated with the closure head, such as, for example, the seismic support platform, the missile shield plate, and the CRDM cooling air circulation system, are disposed upon the closure head within the peripheral envelope thereof and may be moved along with the closure head in an integrated manner when the closure head is either being removed from the reactor pressure vessel or installed thereon.
2. Background of the Invention
Analysis of recent refueling operations has effectively demonstrated the fact that removal and installation of the nuclear reactor pressure vessel closure head is one of the most time-consuming phases or procedures of a nuclear reactor refueling operation. This factor may be readily and better appreciated with reference being made to FIG. 1 of the drawings. As illustrated therein, there is shown a conventional nuclear reactor pressure vessel closure head assembly which comprises the reactor pressure vessel closure head 12 which is secured to the nuclear reactor pressure vessel, not shown, by means of the conventional circumferential array of tension bolts or studs 14. Control rod drive mechanism (CRDM) assemblies 16 pass upwardly through, and extend above, the pressure vessel closure head 12, and cooling baffle assemblies 18 are fluidically connected with the CRDM assemblies 16 so as to provide defined flow paths for cooling air to the CRDM coil stack assemblies, not shown. A lower air manifold 20 is annularly disposed about the upper domed portion of the closure head 12 so as to be disposed beneath the CRDM cooling baffle assemblies 18 and to define a fluidic flowpath in connection therewith. A plurality of vertically extending elbowtype air ducts 22 fluidically connect the lower air manifold 20 with an upper air manifold 24 upon the top of which is disposed a pair of axial flow cooling fans 26. Operation of the axial flow cooling fans 26 therefore causes ambient containment air to be introduced into the cooling baffle assemblies 18 so as to be conducted past the CRDM coil stack assemblies thereby cooling the same. The air is then exhausted into the lower air manifold 20, the elbow air flow ducts 22, the upper air manifold 24, and outwardly from the axial flow fans 26.
A seismic support platform 28 is provided at the upper end of the CRDM assemblies 16 for laterally restraining the CRDM assemblies 16 under seismic conditions, and a conventional cable tray bridge, not shown, is pivotably connected to the facility building walls so as to operationally interface with one of a pair of I-beam structural girders 30 which are supported upon the facility building walls 32. The girders are disposed elevationally above the seismic support platform 28 and serve to support a missile shield block 34 which is disposed atop the girders 30. The shield block 34 serves to protect the containment area and the various other operational components of the reactor from the effects, for example, of a failure within one of the CRDM assemblies 16 whereby a drive rod thereof could possibly be hurled outwardly under the pressurized conditions prevailing within the reactor pressure vessel. The upper air manifold 24 of the CRDM coil stack assembly coolant air flow system is noted as being disposed atop the missile shield block 34.
As a result of the aforenoted structural interrelationship defined between the various operational components of the nuclear reactor, it will then be readily appreciated that when a refueling operation is to be performed in connection with the reactor, an excessive number of man-hours is in fact required to complete such operations. This is due, in part, to the fact that in order, for example, to remove the reactor pressure vessel closure head 12 from the reactor pressure vessel, not shown, a lifting rig or hoist system must be initially installed or affixed to the closure head 12, however, such a lifting or hoisting system cannot even be so attached or affixed to the closure head 12, because of the absence of accessible or available space accommodations, until some of the closure head components are first removed. In particular, for example, the upper air manifold 24, the axial flow cooling fans 26, and the associated elbow air ducts 22 must all be removed. Such removal operations may then be subsequently followed by removal of the missile shield block 34 and the I-beam support girders 30 therefor. A lifting rig and lift rod assemblies may then be installed upon the closure head 12 so as to in fact remove the same from the pressure vessel, not shown, provided, of course, that the closure head tension bolts or studs 14 have been previously de-tensioned and removed. In addition, it was additionally considerably time-consuming to disconnect all of the electrical connections for the individual CRDM power and rod position indicator (RPI) coil assemblies in view of the fact that all of such connections have to be individually disconnected or broken at the sites or locations of all the CRDM assemblies 16 disposed about the closure head 12. In a similar manner, all of the aforenoted procedures attendant the preparation of the reactor for institution of the refueling operations must of course be repeated, in a substantially reverse mode of operation, upon completion of the refueling operations and preparation of the reactor for commencement of normal operations.
An additional time-related factor to also be considered in connection with such conventional reactor facilities, and the drawbacks or operational disadvantages thereof in connection with the performance of refueling operations therefor, is the considerably excessive amount of radiation that the maintenance personnel will tend to be exposed to in view of the considerable amount of time they must spend residing within the vicinity of the closure head 12 during performance of the various aforenoted operations in preparation for, or upon completion of, the refueling operations.
Accordingly, it is an object of the present invention to provide a new and improved nuclear reactor pressure vessel modular closure head assembly.
Another object of the present invention is to provide a new and iproved nuclear reactor pressure vessel modular closure head assembly which can effectively overcome the various operational disadvantages and drawbacks characteristic of conventional nuclear reactor pressure vessel closure head assemblies.
Still another object of the present invention is to provide a new and improved nuclear reactor pressure vessel modular closure head assembly wherein the structural principles thereof are simply applicable or adaptable to conventionally existing nuclear reactor pressure vessel closure head assemblies whereby such conventionally existing closure head assemblies may be modified in accordance with retrofitting techniques.
Yet another object of the present invention is to provide a new and improved nuclear reactor pressure vessel modular closure head assembly wherein all major components operatively associated with the closure head are disposed upon the closure head within the peripheral envelope thereof.
Still yet another object of the present invention is to provide a new and improved nuclear reactor pressure vessel modular closure head assembly wherein all major components operatively associated with the closure head are movable with the closure head in an integrated manner when the closure head is either being removed from, or installed upon, the reactor pressure vessel.
Yet still another object of the present invention is to provide a new and improved nuclear reactor pressure vessel modular closure head assembly wherein the lift rig, tripod sling, and lift rod assemblies are permanently secured to the closure head assembly whereby removal and installation operations for the closure head relative to the pressure vessel can be simply accomplished without removal or dismantling of various operational components associated with the pressure vessel closure head.
A further object of the present invention is to provide a new and improved nuclear reactor pressure vessel modular closure head assembly which substantially reduces the refueling operation time normally required for performance of the refueling cycle, and which is therefore extremely cost-effective.
A yet further object of the present invention is to provide a new and improved nuclear reactor pressure vessel modular closure head assembly which substantially reduces the time required for performance of the refueling operations, particularly the time required for removal and installation of the pressure vessel closure head relative to the pressure vessel, whereby radiation exposure time by means of the maintenance personnel, is reduced substantially.